Mapping for MIMO Communication Apparatus

ABSTRACT

A method, MIMO communication device and electronic storage medium for mapping symbols during a duration of each plural consecutive frames of each of a plurality of first data streams ( 10, 12, 14, 16, 18, 20, 22, 24, 26 ) to frames of a plurality of second data streams (spaced-time coded streams or antenna streams); and varying the mapping during the duration of each of the plural consecutive frames of each of the plurality of first data streams ( 10, 12, 14, 16, 18, 20, 22, 24, 26 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to mapping signals by a multiple input multipleoutput communication apparatus. More specifically, this applicationrelates to an apparatus that maps and a mapping method based on timevarying mapping.

2. Description of the Related Art

Multiple antenna technique has been adopted by many of the emergingcommunication standards, such as 3G cellular systems, the 802.11n systemand 802.16 WiMax systems. See, for example, D. Gesbert et al., “Fromtheory to practice: an overview of MIMO space-time coded wirelesssystems,” IEEE Journal on Selected Areas in Communications, vol. 21, pp.281-301, 2003, the entire contents of which are incorporated herein byreference. Theoretic analysis of communication systems has shown thatdeploying multiple antennas at both the transmitter side and thereceiver side can provide multiple parallel channels to achieve thecommunication of signals. These multiple channels can be used totransmit the same signal to make the transmission less susceptible tochannel fading. This is called diversity gain. On the other hand, thesemultiple channels can be used to transmit different signals at the sametime to increase the transmission rate. This is called multiplexinggain.

Several multiple-input-multiple-output (MIMO) transmission methods havebeen described to achieve these two gains, or a combination thereof.Conventional space-time coded schemes can exploit the diversity gainefficiently but with no or very low multiplexing gain. In contrast, BellLabs Layered Space-Time (BLAST) type transmission schemes can achieve ahigh multiplexing gain but little or no diversity gain. See, forexample, G. J. Foschini, “Layered space-time architecture for wirelesscommunication in a fading environment when using multi-elementantennas,” Bell Labs Technical Journal, vol. 1, no. 2, pp. 41-59, 1996,and P. W. Wolniansky et al., “V-BLAST: An architecture for realizingvery high data rates over the rich-scattering wireless channels,” ProcISSSE-98, Pisa, Italy, September 1998, the contents of both referencesbeing incorporated in their entirety herein by reference.

In communication systems, both kinds of gains may be desirable, though atrade-off needs to be made between the two gains. In various proposalsfor next generation wireless communication standards, such as the IEEE802.11n and the IEEE 802.16e, and 3GPP, several space-time coded schemeshave been proposed for MIMO systems, which can achieve both diversitygain and multiplexing gain, but under certain specific conditions aswill be described later. For example, in an 802.11n scheme, a space-timecoded scheme has been proposed and the proposed scheme is shown in FIG.1 and a more detailed STBC-Antenna-Mapping block diagram is shown inFIG. 2. See also, Tarokh et al., “Space-time codes for high data ratewireless communication: Performance criterion and code construction,”IEEE Trans. Information Theory, vol. 44, no. 2, pp. 744-765, 1998, andTarokh et al., “Combined array processing and space-time coding,” IEEETrans. Information Theory, vol. 45, no 4, pp. 1121-1128, May 1999. Theentire contents of these two references are herein included byreference.

In the scheme shown in FIGS. 1 and 2, the input information bit sequenceis input at an input node 9 and enters through the forward errorcorrection (FEC) encoder 10 and the puncturer 12 to the spatial streamparser 14. The coded bit sequence is split by the spatial parser 14 intoN_(s) parallel spatial streams x₁(n) to x_(Ns)(n). Each stream isinterleaved by a frequency interleaver 16 and then mapped to a symbolstream. Then, the j^(th) symbol stream x_(j), j=1, . . . , Ns, from theQAM (Quadrature Amplitude Modulation) mapping block 18 is parsed intoN_(d) parallel streams x_(j)(i,k), where N_(d) is the number of datasub-channels, j is the spatial stream index, i is the OFDM (OrthogonalFrequency Division Multiplexing) symbol index and k is the datasub-channel index.

Note that the data sub-channels may also be called data-subcarriers. Theword “sub-channels” is used to avoid a confusion between the terms ‘OFDMsubcarriers’ and ‘data subcarriers.’ Symbols from all the spatialstreams, which have the same data sub-subchannel index k (i.e., thestreams x_(j)(i,k), j=1, . . . , Ns) are grouped together and input to aSTBC (space-time block code) encoder 20. The STBC block 20 for acorresponding sub-carrier k outputs Nsts space-time coded streams (i,k),j=1, . . . , Nsts.

Space-time coding schemes are shown in FIGS. 3-5. For example, in FIG.3(A), there is Ns=1 spatial stream and Nsts=2 space-time coded outputstreams. S1 and S2 are symbols from the same spatial stream. A complexconjugate of the symbol S1 is denoted S1* and a negative complexconjugate of the symbol S2 is denoted −S2*. In FIG. 3(B), Ns=2 andNsts=2, the symbol S1 is from the first spatial stream and the symbol S2is from the second spatial stream. FIGS. 3(A) and (B) show variouspossible mappings of the symbols S1 and S2 to the multiple antennas.

In FIG. 4(A), Ns=2 and Nsts=3, the symbols S1 and S2 are from the firstspatial stream while the symbols S3 and S4 are from the second spatialstream. In FIG. 4(A), Ns=3 and Nsts=3, the symbol 51 is from the firstspatial stream, the symbol S2 is from the second spatial stream, and thesymbol S3 is from the third spatial stream. It is noted again variouspossible mappings of the symbols of the spatial streams to the multipleantennas.

In FIG. 5(A), Ns=2 and Nsts=4, the symbols S1 and S2 are from the firstspatial stream while the symbols S3 and S4 are from the second spatialstream. In FIG. 5(B), Ns=3 and Nsts=6, the symbols S1 and S2 are fromthe first spatial stream, the symbols S3 and S4 are from the secondspatial stream, and the symbols S5 and S6 are from the third spatialstream. Again, it is noted various possible mappings of the symbols ofthe spatial streams to the multiple antennas.

The Nsts space-time coded streams that are output for each datasub-channel k are then passed through an antenna mapping unit 4 thatapplies a matrix P_(k) to each sub-carrier. The output of the antennamapping unit 4, after applying the matrix P_(k), is given by:

[{tilde over (x)}_(l)(i,k), . . . , {tilde over(x)}_(Ntx)(i,k)]^(T)=P_(k)[{circumflex over (x)}₁(i,k), {circumflex over(x)}₂(i,k), . . . , {circumflex over (x)}_(Nsts)(i,k)]^(T),  (1)

where “T” denotes a vector transpose operation.

Different sub-carriers may use the same or different antenna mappingmatrices P_(k). These matrices are fixed within a transmission frame ora sub-frame, which are basic units of data transmission. In other words,the mapping is constant or fixed during the duration of each frame. Asub-frame is also referred to as a Transmission Time Interval (TTI) in3GPP. In Release 6 of 3GPP, a sub-frame (or TTI) consists of 3 timeslots and has a fixed duration of 2 milli-seconds. In IEEE 802.11n, eachframe includes a multiple access (MAC) header, which comprises framecontrol information, address, and sequence control information. In802.11n, the frame has a variable length body, which containsinformation specific to the frame type, and an error correcting code.The terms frame and sub-frame are used interchangeably.

For example, in the four transmit antennas case, a 4×4 Walsh-Hadamardmatrix, P, shown below, can be used as P_(k) for all the datasub-channels.

$P = {{\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}}.}$

Then, the symbols {tilde over (x)}_(j)(i,k), k=1, . . . , N_(d), aregrouped together and input to an IFFT (inverse fast Fourier transform)conversion unit 22 to generate the time domain transmission signals. Thetime domain transmission signals are then amplified by a gatedintegrated amplifier (GI) 24 and transformed in analog signals by analogblock 26 and the analog signals are output at the output terminals ofthe plurality of transmit antennas 6.

Due to space-time coding, this scheme can achieve the diversity gain. Asthe scheme can also transmit multiple spatial symbol streamssimultaneously from the multiple QAM blocks 18, the scheme can alsoachieve the multiplexing gain.

At the receiver side (not shown), which is compatible with thetransmitter side shown in FIG. 1, the signals received from the multiplereceive antennas of the receiver, after down-conversion to base-band,are first input to a demodulator.

The received signal is not free of noise and also is distorted by thechannel. Soft or hard decisions of the corresponding bit streams arethen generated. The output of a hard decision is whether the bitreceived is a ‘0’ or ‘1’. On the other hand, the output of a softdecision is a probability (or a compatible measure) that the bit is a‘0’ or ‘1’. The decision streams, which carry soft or hard decodinginformation, are then de-interleaved, de-multiplexed, and, finally,input to the channel code decoder to recover the input information bitstream.

When spatial multiplexing is used and the input symbols are equallylikely, the optimal demodulation scheme, which is the maximum-likelihood(ML) demodulation scheme, needs to detect the symbols from all thespatial streams jointly. This makes the ML demodulation schemeprohibitively complicated and thus infeasible for practical systemimplementation. Thus, linear demodulation schemes, such as linearminimum mean square error estimator (LMMSE) or linear zero-forcing (ZF)estimators are usually used in practical implementations. Theseestimators pass the input signal vector through a spatial filter thatgenerates the estimated symbols for each spatial stream independently.The spatial streams can be demodulated separately, or can be demodulatedusing a successive interference cancellation (SIC) receiver, or itsvariants.

It is noted that in such receivers, the multiple streams interfere witheach other. Therefore, the estimated signals of different spatialstreams may have different Signal-to-Interference-Noise-Ratio (SINR)s.The spatial streams with high SINR are more reliable than the spatialstreams with low SINR, and lead to lower bit error and frame errorrates. These SINRs depend on the channel matrix H, which relates to thelinks between the multiple transmitting antennas and the receivingantenna(s), and the matrix P, which is the mapping matrix between thespace-time coded spatial streams and the transmit antennas. The spatialstream with the lower SINR is often the performance bottleneck anddetermines the overall performance of the system.

In the MIMO scheme discussed above, the antenna mapping matrix P isfixed, i.e., constant in time. This lack of change of the matrix P leadsto a performance loss when linear receivers are used. Due to the channelrealization, if one of the estimated spatial streams has a very lowSINR, there is no mechanism available for the conventional scheme with afixed matrix P to improve its SINR.

In fact, if the channel is slowly time-varying, it can be assumed thatthe channel matrix is fixed within each transmission frame. Thus, theoutput SINR of each estimated spatial stream does not vary over timeduring a frame. This is true, for example, in the IEEE 802.11n system,because the OFDM symbol duration is only 4 μs, while the Dopplerfrequency shift of a typical 802.11n channel model is about 5 Hz, whichcorresponds to a coherence duration (the duration over which the channelremains almost the same) of 80 milli-seconds. One option is to use longchannel codewords that span multiple coherence intervals of the channel.However, for relatively low Doppler frequencies, this is not a feasibleoption due to the long codeword lengths required.

For example, in FIG. 4(A), the first spatial stream is space-time codedand the output space-time coded streams are mapped to the transmitantennas TX1 and TX2. The second spatial stream is directly mapped tothe transmit antenna TX3. This mapping is fixed within a transmissionframe. If the channel does not vary significantly within a frame, theSINR of the received spatial streams is also fixed. The second spatialstream (S2) is not space-time coded, has a lower diversity order and ismore susceptible to harsh channel fades. Therefore, close to one halfthe total number of transmitted symbols are more often fading and have alower SINR. This makes it hard for the channel decoder to recover theoriginal information bits. An almost static channel and theunavailability of time domain diversity within each frame, thus leads tohigher frame error rates in the conventional scheme.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a MIMO communicationmethod of wireless communication via a plurality of antennas andelectronic storage medium are disclosed. The method includes mappingsymbols during a duration of each plural consecutive frames of each of aplurality of first data streams to frames of a plurality of second datastreams; and varying the mapping during the duration of each of theplural consecutive frames of each of the plurality of first datastreams.

According to another aspect of the present invention, a MIMOcommunication device for wireless communication via a plurality ofantennas is disclosed. The MIMO communication device includes aplurality of antennas; plural processing devices coupled to theplurality of antennas; and a mapping unit configured to map symbolswithin each frame of a plurality of data streams between different ofantennas and the processing units and configured to varyingly map thesymbols during a duration of each of plural consecutive frames.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a block diagram for a space-time coded scheme forconventional 802.11n MIMO systems;

FIG. 2 shows a block diagram of a conventional STBC-antenna-mappingblock used in FIG. 1;

FIGS. 3(A)-(B) show a conventional STBC for two transmit antennas;

FIGS. 4(A)-(B) show a conventional STBC for three transmit antennas;

FIGS. 5(A)-(B) show a conventional STBC for four transmit antennas;

FIG. 6(A) shows a block diagram of a transceiver that includes atransmitter portion and a receiver portion according to one embodimentof the invention;

FIG. 6(B) shows a block diagram of a transceiver having a coding blockinserted between a mapping unit and a plurality of antennas according toanother embodiment of the invention;

FIG. 6(C) shows a block diagram of the transmitter portion of thetransceiver shown in FIG. 6(A);

FIG. 6(D) shows a block diagram of the receiver portion of thetransceiver shown in FIG. 6(A);

FIG. 6(E) shows a detailed block diagram of the receiver shown in FIG.6(D);

FIG. 7 is a block diagram of a single carrier space-time codedtransmitter portion of the transceiver according to another embodimentof the invention;

FIG. 8 is a block diagram of a multiple carrier MIMO-OFDM transmitterportion of the transceiver according to another embodiment of theinvention; and

FIGS. 9-14 are graphs showing frame error rates with and without antennahopping with various encoding methods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, accordingto the embodiment shown in FIG. 6(A), a transceiver 1 is shown to have atransmitter portion 2 and a receiver portion 3. The transceiver 1 ispart of a MIMO communication apparatus according to an embodiment of theinvention. An antenna mapping unit 4 is connected to multiple antennas 6for both the transmitter 2 and receiver 3 portions. In anotherembodiment of the invention shown in FIG. 6(B), an intermediate block 8,for example, a unitary or not-unitary precoding block or a beamformingblock or an antenna selection block or any combination of these blocksis connected between the antenna mapping unit 4 and the multipleantennas 6. It is noted that although FIG. 6(A) shows the transceiver 1having the transmitter and the receiver portions, each of thetransmitter and receiver portions can be implemented to function as astand alone device. For this reason, it is understood in the followingthat the term “communication device” refers to any of a transmitter, areceiver, or a transceiver and thus, the mapping method described nextapplies to the communication device. It is also noted that thetransmitter, the receiver, and the transceiver can be implemented, forexample, as a base station that is part of the MIMO communicationsystem, as a mobile communication terminal, or as any known device thatexchanges data with another device. The mapping method described nextalso applies to any communication protocol used by the transmitter,receiver, and/or transceiver, as for example 3G cellular systems, the802.11n systems and the 802.16 WiMax systems. The mapping method is notlimited to the above known systems, but is applicable to any system thatmaps signals. Also, the method can be implemented in an apparatus thatis part of a network which does not implement the method. For example, amobile communication terminal can support the mapping method describednext even if the base stations constituting the network do not supportthe mapping method, and vice versa.

In the following, a description of transmitting a signal by thetransmitter portion 2 of the transceiver 1 is explained in more detailwith regard to FIG. 6(C). The embodiment of FIG. 6(C) is not limited tothe transmitter portion 2 of the transceiver 1 shown in FIG. 6(A) but isunderstood to also apply to a stand alone transmitter.

According to FIG. 6(C), a signal to be transmitted by the transmitterpart 2 of the transceiver 1 is encoded into multiple streams, eachstream including multiple frames. A frame or a sub-frame is a basiccontinuous transmission unit. Each frame includes a plurality ofsymbols. A sub-frame is also referred to as a Transmission Time Interval(TTI) in 3GPP. In Release 6 of 3GPP, a sub-frame (or TTI) consists of 3time slots and has a fixed duration of 2 milli-seconds. In IEEE 802.11n,each frame includes multiple access (MAC) header, which comprises framecontrol information, address information, and sequence controlinformation. In 802.11n, the frame has a variable length body, whichcontains information specific to the frame type, and an error correctingcode; the maximum length of a frame at the MAC layer is 8191 bytes. TheIEEE 802.16 standard specifies a frame duration of 5 ms. The terms frameand sub-frame are used interchangeably.

Each of the symbols is mapped to the multiple antennas 6, for examplebased on an equivalent mapping matrix {circumflex over (P)}, whilevarying the equivalent mapping matrix {circumflex over (P)} over aduration of a single frame or each of plural consecutive frames, so thatthe symbols of each frame are mapped to different frames of differentantenna streams that are transmitted by different antennas of themultiple antennas 6. In other words, symbols within each of pluralconsecutive frames of each of first data streams (space-time codedstreams or antenna streams in FIG. 6(C)) are mapped to frames of aplurality of second data streams (space-time coded streams or antennastreams in FIG. 6(C)). The mapping is varied during the duration of eachof the plural consecutive frames of each of the plurality of first datastreams. One example of mapping as noted above is based on theequivalent mapping matrix. However, other mappings know by one ofordinary skill in the art may be used, as for example a pseudo-randomsequence. For the sake of simplicity, the mapping based on theequivalent mapping matrix is discussed next but the invention is notlimited to this mapping.

The first data streams may be generated by processing units (any one orcombination of elements 10, 12, 14, 16, 18, 20, 22, 24, and 26 in FIG.6(C)) and the mapping may be performed by the mapping unit 4.Optionally, when a communication device includes the transmitter portionshown in FIG. 6(C) and functions as a transmitter, an input signal isinput to an input terminal 9 of the communication to be encoded by theencoder 10 prior to being mapped by the mapping unit 4. Also, the mappedantenna streams may be converted to ‘time domain’ signals by theconversion unit 22. If the communication device discussed abovefunctions as a receiver as shown in FIG. 6(D), then, optionally, thecommunication device receives plural signals at the plurality ofantennas and the fast Fourier transform (FFT) conversion unit 22converts the received signals to the frequency domain to produce pluralantenna data streams for mapping by the mapping unit 4. In addition, themapped streams may be decoded by decoder 10 to generate an outputsignal. In another embodiment, the communication device functions as atransceiver and each unit and step discussed above with reference to thecommunication device functioning as the transmitter or the receiver arepart of the transceiver.

A description of receiving a signal by the receiver portion 3 of thetransceiver 1 is the reverse of the transmitting description as will beunderstood by one of ordinary skill in the art. FIG. 6(D) shows a blockdiagram of the receiver portion 3 of the transceiver 1 shown in FIG.6(A). Multiple (but different) copies of the transmitted signal arereceived by the multiple antennas 6. These copies of the signal areamplified by a low noise amplifier, bandpass filtered to remove out ofband noise, down-converted to baseband, and digitally sampled by ananalog to digital converter (ADC). As will be appreciated by personsskilled in the art, the digital sampling need not always happen atbaseband. An intermediate frequency version of the signal may also bedigitally sampled and then processed. The signal received in a guardinterval is discarded, and is followed by an FFT block processing. Themultiple received streams are then passed to a MIMO demodulation block 4that performs the task of extracting the data transmitted from themultiple received signals. The MIMO demodulation block 4 removespre-coding, does antenna demapping, deinterleaving, FEC decoding anddemodulation as shown in FIG. 6(E).

As will be appreciated by persons skilled in the art, it is advantageousto often combine the various tasks such as precoding, demapping, FECdecoding to improve receiver performance. FIG. 6(E) shows a general MIMOdemodulation block 4 in which these processes can happen serially, aswas shown in FIG. 6(C), or together. FIG. 6(E) shows optional pre-FFTestimator block 28, frequency offset correction block 30, post-FFTestimator block 32, a pilot removal block 34, a demultiplexing block 36,and channel decoders 38. In addition, FIG. 6(E) shows optional analogfront-end blocks 40.

Compared to a conventional space-time coded transmission scheme, inwhich a signal mapping matrix is fixed during the duration of a frame,i.e., the mapping matrix P shown in FIG. 1 is constant over the durationof the frame, a new mapping in which the mapping is not fixed during theframe or plural consecutive frames is described next.

The novel mapping method involves changing intentionally and in apredefined manner, the mapping between symbols of space-time encodedstreams and symbols of the plural antenna streams that correspond to theplurality of antennas 6. The mapping is performed during the singleframe or each of plural consecutive frames, so that a SINR of eachestimated spatial stream changes from one space-time coded block toanother space-time coded block during the duration of the same frame.

By changing the mapping during the duration of the single frame or eachof the plural consecutive frames in the transmitter portion 2, areceiver portion of another transceiver, which receives the signals fromthe transmitter portion 2 of the transceiver 1, “sees” a “time-varying”channel, and can exploit a time-diversity of the channel to improve adecoding performance. It is noted that this new mapping method isimplemented in this embodiment as an open loop method as the method doesnot require feedback information from the receiver portion of the othertransceiver.

However, in another embodiment of the invention the method is implementbased on a closed-loop mechanism, such that the transmitter portion ofthe transceiver 1 requires feedback information from the receiverportion of the other transceiver that receives the information from thetransceiver 1. The information is used to change the mapping matrixdynamically. A closed-loop feedback 5 unit performs the task ofconverting the received feedback into information used by the STBC 20 inFIG. 6(C) or block 8 in FIG. 6(D), for example.

The mapping method described based on the transmitter portion 2 shown inFIG. 6(C) achieves a high performance even when used in a conventionalsystem and does not always require any alterations in for training,automatic gain control (AGC) settings, etc.

Although a random beamforming scheme varies transmit amplitudeassociated to the transmitted streams in a pre-determined fashion, therandom beamforming scheme is different from the method of thisembodiment because the random beamforming scheme is designed formulti-user diversity. The random beamforming is designed to select oneout of many possible nodes for transmission and requires feedback aboutthe channel state from all the nodes. Thus, the random beamformingscheme is not a time-diversity enhancing technique, unlike the newmethod of the embodiment of this invention.

The equivalent mapping matrix {circumflex over (P)} of the embodimentshown in FIG. 6(C) changes over the duration of the single frame or eachof the plural consecutive frames, according to a predefined patternassigned to that the single frame or to each of the plural consecutiveframes. Examples of the predefined pattern are shown below. However, thepossible predefined patterns are not limited to those examples. Anyvariation of the equivalent mapping matrix during the single frame orthe plural consecutive frames can be used as the predefined pattern.Also, the changing of the equivalent matrix may have a periodicitywithin the single frame or across the plural consecutive frames.

The predefined pattern can be exchanged between the transmitter portionof the transceiver 1 and the receiver portion of the other transceiverat the beginning of the communication, or can be transmitted to thereceiver portion of the other tranceiver by the transmitter portion ofthe transceiver 1 during each frame or during each frame of the multipleframes. The receiver portion of the other transceiver may also determinethe predefined pattern on its own without any assistance from thetransmitter portion of the transceiver 1.

The transmitter portion 2 shown in FIG. 6(C), instead of using a fixedantenna mapping matrix P, as the conventional art does, uses the timevarying equivalent mapping matrix {circumflex over (P)}. For example,the equivalent mapping matrix {circumflex over (P)} of the transmitterportion 2 of FIG. 6(C) may include (1) a space-time encoded spatialstream permutation matrix S(i) that is applied by a unit 610, and/or(ii) an antenna mapping (spatial steering) matrix P(i) that is appliedby a unit 620, and/or (iii) a transmit antenna permutation matrix T(i)that is applied by a unit 630 to the spatial streams. A permutationcontroller 640 may include a matrix combining unit configured to decidewhich combination of the matrixes (1)-(3) is selected. Alternatively,the permutation controller 640 itself decides which combination of thematrixes (1)-(3) to be used. All of the matrices may vary according tothe pre-defined pattern over the duration of the single frame or theplural consecutive frames, i.e., the matrices are functions of thespace-time block index i in a single transmission frame. In anotherembodiment, the equivalent mapping matrix {circumflex over (P)}cyclically varies over the duration of the single frame or the pluralconsecutive frames.

The matrices S, P, and T are only required to be non-singular, but it isoften advantageous to make the matrices unitary or semi-unitary. Anon-singular mapping unit and a unitary or semi-unitary mapping unitthat are part of the mapping unit 4 decide which kind of mapping matrixto be applied. By way of example, the term “unitary” matrices is used inthe following, without restricting the invention to this specific case.Also, it is possible to make any of the S and T matrices an identitymatrix. According to one embodiment of the present invention, S(i) is anNs by Ns unitary matrix, where Ns is the number of space-time codedspatial streams, and the matrix S(i) belongs to a set Ω. The matrix P(i)is an Ns by Nt semi-unitary matrix, where Nt is the number of transmitantennas, and P(i) belongs to the set Φ. T(i) is an Nt by Nt unitarymatrix and belongs to the set Ψ.

The permutation controller 640 of the transmitter portion 2 selects thepermutation matrices S(i), P(i) and T(i) for the i-th space-time codedblock transmission based on the pre-defined permutation pattern, whichis also known to the receiver portion of the other tranceiver. Thepermutation controller 640 changes, over the duration of the singleframe or each of the plural consecutive frames, one of the S, P, and Tmatrices, a combination of the S, P, and T matrices, or all thematrices. More specifically, the permutation controller 640 changes oneof the matrices S, P, T, SP, ST, PT, SPT. The matrices can be changedconcurrently or one at a time. In this way, the product of the S, P andT matrices changes over the duration of the single frame or the pluralconsecutive frames.

In another embodiment, the permutation controller 640, over the durationof the single frame or each of the plural consecutive frames, changesone or a plurality of the matrices included into the equivalent mappingmatrix {circumflex over (P)} a number of times that is equal to thenumber of antennas. However, for practical reasons or due to thespecific structure of the STBC, the permutation controller 640 changesone or the plurality of the matrices included into the equivalentmapping matrix {circumflex over (P)} a number of times that is less thanor greater than the number of antennas. According to one embodiment ofthe present invention, the equivalent mapping matrix changes at leasttwice during the single frame or each of the plural consecutive frames.

In still another embodiment, sub-carrier generating units (for exampleblock 18) of the processing units feeding data streams to the mappingunit 4 may generate plural sub-carrier data streams and the mapping unit4 may apply a plurality of matrices P, to the plural sub-carrier datastreams (see for example FIG. 2) when the mapping unit is used in atransmitter or a transceiver. It is noted that the same plurality ofmatrices may be applied to the antenna streams received from theplurality of antennas 6 when the mapping unit is used in a receiver or atransceiver.

According to another embodiment of the invention, the time-dependentequivalent antenna mapping matrix is given by

{circumflex over (P)}(i)=S(i)P(i)T(i).

The equivalent channel matrix seen by the receiver portion of the othertransceiver is an Ns by Nr matrix, where Nr is the number of thereceiver antennas, and the Ns by Nr matrix is given by:

Ĥ(i)={circumflex over (P)}(i)H=S(i)P(i)T(i)H.

Due to the time variance of the equivalent mapping matrix {circumflexover (P)}(i) in the transmitter portion 2, the channel “seen” by thereceiver portion of the other transceiver also varies over the durationof the frame or the plural consecutive frames, even when the channelmatrix H does not vary in time. This time variation of the matrix{circumflex over (P)} introduces the time diversity lacking in theconventional methods, which leads to an improved performance of thetransmitter portion of the transceiver. All the properties discussedabove with regard to the equivalent mapping matrix {circumflex over (P)}of the transmitter portion 2 equally apply to a mapping matrix used byany of a standalone receiver device or a receiver portion of anothertransceiver. It is noted that although the receiver portion is differentthan the transmitter portion, both of the receiver and transmitterportions may have an identical mapping matrix block. However, the S, P,and T matrices might be different at the receiver portion as illustratedin FIG. 6(D) than at the transmitter portion.

At the receiver portion of the other transceiver, the sets Ω, Φ, and Ψand the permutation pattern are known as described above. However, ifthe pseudorandom sequence is used, each interval (chip duration) of thepseudorandom sequence leads to a new matrix (or matrices). Thesematrices belong to a larger set of Ω, Φ, and ψ, and lead to a differentperiodic permutation pattern.

If the matrix T(i) or the matrix P(i) is time varying, the receiverneeds to estimate an Nt by Nr channel matrix H to track the Ĥ(i).However, in the conventional scheme, the receiver portion of thetransceiver only needs to estimate the equivalent “channel matrix” P H,which is an Ns by Nr matrix. In some cases, Ns is less than Nt, whichimplies that the new scheme will introduce some estimation complexitywhen the matrix T(i) or the matrix P(i) is time-varying.

In order to avoid this increase in complexity, the matrices P and T canbe fixed in time and only the matrix S(i) is allowed to vary in timeaccording to the predefined pattern. In that case, the receiver portionof the other transceiver only needs to estimate the equivalent “channelmatrix” P T H, which is also an Ns by Nr matrix.

The above described mapping method can be implemented in an apparatusfor mapping signals in a wireless communications network. For example,the apparatus has a mapping unit 4 connected between a coder 10 and aplurality of antennas 6. The coder is configured to process a pluralityof data streams in parallel and in which each data stream is partitionedinto a plurality of frames and each frame includes a plurality ofsymbols. Each antenna is inserted in a wireless channel for carrying oneof the plurality of streams. The mapping unit is configured to switchdifferent symbols in the frames between different antennas and thecoding unit according to the mapping matrix while each channel iscarrying the corresponding data stream. The above described apparatuscan be, for example, a transmitter, a receiver, or a transceiver.

EXAMPLES

First, in FIG. 5(A), for the 4 transmit antennas, with Ns=2 spatialstreams, and Nsts=4 space-time coded streams, the T and P matrices canbe fixed to be 4×4 identity matrices. Thus, the set Ω consists of 3elements defined as:

$\Omega = {\begin{Bmatrix}{{S_{0} = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},{S_{1} = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 0 & 1\end{bmatrix}},} \\{S_{2} = \begin{bmatrix}1 & 0 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1 \\0 & 1 & 0 & 0\end{bmatrix}}\end{Bmatrix}.}$

One example of the predefined permutation pattern, which permutesthrough all the elements of Q, is:

S(i)=S_(mod(i,3)).

Any known permutation that permutes through all the elements of Ω overthe duration of the frame or plural consecutive frames can be used.Other permutation operations or methods for changing the value of thematrix S over the duration of the single frame (or over the duration ofthe plural consecutive frames) can be used as long as the receiverportion of the transceiver is made aware of, or learns by itself, thetransmitter portion's predefined permutation pattern.

For the 3 transmit antennas, Ns=2 spatial streams, and Nsts=3 space-timecoded streams case shown in FIG. 4(A), the permutation pattern issimilar to the previous example. Thus, the set Ω can be defined as:

$\Omega = {\begin{Bmatrix}{{S_{0} = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}},{S_{1} = \begin{bmatrix}1 & 0 & 0 \\0 & 0 & 1 \\0 & 1 & 0\end{bmatrix}},} \\{S_{2} = \begin{bmatrix}0 & 0 & 1 \\1 & 0 & 0 \\0 & 1 & 0\end{bmatrix}}\end{Bmatrix}.}$

For the 4 transmit antennas, 3 spatial streams, and 4 space-time codedstreams case shown in FIG. 5(B), the set Ω and the permutation patterncan be defined similar to the one defined in the 4 transmit antennas and2 spatial streams case.

In the above examples, all the S matrices are permutation matrices(having elements 1 or 0, with at most one element being 1 in any givenrow or column), which means that the S matrices only permute the inputspace-time coded spatial streams without affecting the weight that isattributed to the space-time coded spatial streams. Using permutationmatrices in the antenna mapping block 4 has the advantage that thematrices do not need any changes for the AGC operation. The complexityof the channel estimation and other system design parameters arecomparable with the conventional scheme, which does not use the timevarying permutation according to the embodiments of the invention.

In multi-carrier communication systems, such as an 802.11n WLAN OFDMsystem, the new mapping method of the embodiment discussed with regardto FIG. 6(C) can be implemented at least in two ways:

-   [1] Space-time coded OFDM symbol block based: In this scheme, all    the sub-carriers in the same space-time code OFDM symbol use the    same permutation matrices S(i), P(i) and T(i), which are only    functions of the space-time coded OFDM block index i. The above    examples are based on this scheme.-   [2] Sub-carrier based: In this scheme, different sub-carriers in the    same space-time coded OFDM symbol block use different permutation    matrices S(i, k), P(i, k) and T (i, k), which are the functions of    both the space-time coded OFDM block index i and the sub-carrier    index k. For example, for the sub-carrier based schemes, the    following predefined permutation pattern can be used:

S(i,k)=S_(mod(i+k,3)).

Other predefined permutation patterns can be used as discussed above.

The new method of mapping can be also used for single carrier MIMOsystems. For example, a single carrier MIMO system may have thetransmitter portion as shown in FIG. 7. The predefined permutationpattern defined in the above example can be used directly for thissingle carrier MIMO system.

There are possible variations of the above discussed mapping method. Theapproach proposed above can be used for both single carrier andmulti-carrier MIMO systems, which include the WiMax 802.16 systems, WLAN802.11n systems, 3GPP and other communication systems. Although in theabove discussed examples, only permutation matrices have been used, anyunitary, or even non-singular matrices can be used as S, T and Pmatrices of the new mapping method.

While the block diagrams of FIGS. 6(A)-7 show only one channel code, themapping method is also applicable to transmitter portions with multiplecodewords. One example of such transmitter portion with multiplecodewords is shown in FIG. 8, which is applicable for two or morespatial streams cases.

The new mapping method can be also applied to other systemconfigurations and other space-time coding or spatial multiplexingschemes, for example, BLAST systems with independent channel encoded fordifferent spatial streams, and/or other systems know to one of ordinaryskill in the art.

Simulations Results

Simulation results are shown below to illustrate the performanceadvantage of the scheme of the present invention.

1. Case 1—Single carrier MIMO system simulation results.

The structure used for this simulation is shown in FIG. 7 and an antennahopping pattern can be any of the predefined permutation patterns givenin the above examples. The simulation parameters are listed as follow:

Channel Model i.i.d. Rayleigh flat fading channel Number of TX 4 Numberof RX 2 STBC See FIG. 5(A) Demodulator LMMSE soft demodulator withoutSIC FEC ½, ¾ LDPC codes FEC decoder BP soft decoder with 30 iterationsChannel seeds 10000 Modulation 16QAMFrom the slopes of the FER (frame error rate) curves shown in FIG. 9, itcan be seen that the new scheme achieves a higher diversity gaincompared with the conventional scheme without antenna hopping. In thisconfiguration, the new scheme achieves about more than 1.5 dB gain at aframe error rate of 0.01. For ¾ LDPC coded case shown in FIG. 10, thenew scheme can achieve about 2.3 dB gain at the frame error rate of0.01.

2. Case 2. MIMO-OFDM System Simulation Results

The structure of the system used in this simulation is shown in FIG.6(C) and the antenna hopping pattern can be any of the patterns given inthe above examples. The simulation parameters are listed as follow:

Channel Model TGn channel B Number of TX 4 Number of RX 2 STBC See FIG.5(A) Demodulator LMMSE soft demodulator without SIC FEC ½, ¾ LDPC codesand convolutional codes FEC decoder BP soft decoder with 30 iterationsfor LDPC and softViterbi for CC Channel seeds 10000 Modulation 16QAMFrom the simulation results shown in FIG. 11, it can be seen that thenew scheme achieves more than 1 dB gain for all modulation codingsettings (MCS) comparative to the situation without antenna hopping.Similarly, FIGS. 12-14 show the gain achieved by the various embodimentsof the present invention when quadraphase-shift modulation is used.

The present invention includes processing of a signal input to thetransmitter portion or received at the receiver portion, and programs bywhich the input signal is processed. Such programs are typically storedand executed by a processor in a mobile wirelessreceiver/transmitter/transceiver implemented in VLSI. The processortypically includes at least processor storage product, i.e., anelectronic storage medium, for storing program instructions containingdata structures, tables, records, etc. Examples are storage media,electronic memories including PROMs (EPROM, EEPROM, flash EPROM), DRAM,SRAM, SDRAM, FRAM, or any other magnetic medium, or any other mediumfrom which a processor can read, for example compact discs, hard disks,floppy disks, tape, magneto-optical disks.

The electronic storage medium according to one embodiment of theinvention may include one or a combination of processor readable media,to store software employing computer code devices for controlling theprocessor. The processor code devices may be any interpretable orexecutable code mechanism, including but not limited to scripts,interpretable programs, dynamic link libraries (DLLs), Java classes, andcomplete executable programs. Moreover, parts of the processing may bedistributed for better performance, reliability, and/or cost.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A MIMO (multiple-input multiple-output) communication method forwireless communication, comprising: mapping symbols during a duration ofeach plural consecutive frames of each of a plurality of first datastreams to frames of a plurality of second data streams; and varying themapping during the duration of each of the plural consecutive frames ofeach of the plurality of first data streams.
 2. The method of claim 1,comprising: encoding an input signal to generate the plurality of firstdata streams.
 3. The method of claim 2, comprising: converting theplurality of second data streams to time domain signals to be applied toa plurality of antennas.
 4. The method of claim 1, comprising: receivingsignals from a plurality of antennas and converting the received signalsinto the frequency domain to produce the plurality of first datastreams.
 5. The method of claim 4, further comprising: decoding thesecond data streams after the mapping.
 6. The method of claim 1,wherein: when transmitting an input signal via a plurality of antennas,encoding an input signal to generate the plurality of first datastreams, and when receiving signals by the plurality of antennas,converting the received signals from the plurality of antennas tofrequency domain signals to produce the plurality of first data streamsfrom the plurality of antennas.
 7. The method of claim 6, furthercomprising: when transmitting the input signal via the plurality ofantennas, converting the mapped second data streams to time domain datastreams applied to the plurality of antennas, and, when receiving thesignals from the plurality of antennas, decoding the mapped second datastreams.
 8. The method of claim 1, wherein the mapping step comprises:mapping the symbols within each of the plural consecutive frames of eachof the first data streams based on a combination of a mapping matrix andat least one of a space-time coded spatial stream permutation matrix anda transmit antenna permutation matrix.
 9. The method of claim 8, whereinthe varying step comprises: varying one or more of the mapping matrix,the space-time coded spatial stream permutation matrix, and the transmitantenna permutation matrix during the duration of each of the pluralconsecutive frames.
 10. The method of claim 1, wherein the mapping stepcomprises: performing closed loop mapping of each first data stream. 11.The method of claim 1, wherein the mapping step comprises: mapping thesymbols of the plurality of first data streams based on a non-singularmatrix.
 12. The method of claim 1, wherein the mapping step comprises:mapping the symbols of the plurality of first data streams based on aunitary or a semi-unitary matrix.
 13. The method of claim 1, wherein thevarying step comprises: permuting one or more of the mapping matrix, thespace-time coded spatial stream permutation matrix, and the transmitantenna permutation matrix over the duration of each of the pluralconsecutive frames.
 14. The method of claim 1, wherein the varying stepcomprises: varying one or more of the mapping matrix, the space-timecoded spatial stream permutation matrix, and the transmit antennapermutation matrix over the duration of each of plural consecutiveframes at least twice.
 15. The method of claim 1, wherein the varyingstep comprises: varying one or more of the mapping matrix, thespace-time coded spatial stream permutation matrix, and the transmitantenna permutation matrix with a periodicity that extends over at leasttwo consecutive frames.
 16. The method of claim 1, wherein: the mappingstep comprises generating plural sub-carrier data streams and mappingthe plural sub-carrier data streams with a plurality of matrices.
 17. AMIMO (multiple-input multiple-output) communication device for wirelesscommunication, comprising: a plurality of antennas; plural processingdevices coupled to the plurality of antennas; and a mapping unitconfigured to map symbols within each frame of a plurality of datastreams between different antennas and the processing units andconfigured to varyingly map the symbols during a duration of each ofplural consecutive frames.
 18. The device of claim 17, in which theprocessing units comprise encoders configured to encode the symbols, andthe antennas transmit the mapped symbols.
 19. The device of claim 17, inwhich the plurality of antennas receive the symbols, and the processingunits comprise decoders configured to decode the symbols.
 20. The deviceof claim 17, in which the mapping unit is configured to time varyinglymap the symbols with a periodicity that extends over at least twoconsecutive frames.
 21. The device of claim 17, wherein: the processingunits, when transmitting an input signal via the plurality of antennas,comprise, an encoder configured to encode an input signal to generatethe plurality of data streams, and a conversion unit configured toconvert the mapped symbols into time domain data streams applied to theplurality of antennas; and the processing units, when receiving signalsfrom the plurality of antennas, comprise, conversion units configured toconvert the received signals received by the plurality of antennas intofrequency domain signals to generate the plurality of data streams formapping by the mapping unit, and a decoder configured to decode thesymbols subjected to mapping by the mapping unit.
 22. The device ofclaim 17, wherein the mapping unit comprises: a matrix combining unitconfigured to map the symbols within each of the plural consecutiveframes of each of the plurality of data streams based on a combinationof a mapping matrix and at least one of a space-time coded spatialstream permutation matrix and a transmit antenna permutation matrix. 23.The device of claim 22, wherein the matrix combining unit is configuredto vary one or more of the mapping matrix, the space-time coded spatialstream permutation matrix, and the transmit antenna permutation matrixover the duration of each of the plural consecutive frames of theplurality of first data streams.
 24. The device of claim 17, wherein themapping unit comprises: a closed loop mapping unit configured to performclosed loop mapping of each symbol.
 25. The device of claim 17, whereinthe mapping unit comprises: a non-singular mapping unit configured tomap the symbols of the plurality of data streams based on a non-singularmatrix.
 26. The device of claim 17, wherein the mapping unit comprises:a unitary or semi-unitary mapping unit configured to map the symbols ofthe plurality of data streams based on a unitary or a semi-unitarymatrix.
 27. The device of claim 17, wherein the mapping unit comprises:a permuting unit configured to permute at least one of the mappingmatrix, the space-time coded spatial stream permutation matrix, and thetransmit antenna permutation matrix within the duration of each of theplural consecutive frames.
 28. The device of claim 17, wherein themapping unit is configured to vary the at least one matrix at leasttwice during the duration of each of the plural consecutive frames. 29.The device of claim 17, wherein: the processing units comprisesub-carrier generating units configured to generate plural sub-carrierdata streams; and the mapping unit comprises sub-carrier mapping unitsconfigured to map symbols of the plural sub-carrier data streams with aplurality of matrices.
 30. A MIMO (multiple-input multiple-output)communication device for wireless communication, comprising: a pluralityof antennas; plural processing devices coupled to the plurality ofantenna; and means for mapping symbols within each frame of a pluralityof data streams between different antennas and the processing units andfor varyingly mapping the symbols during a duration of each of pluralconsecutive frames.
 31. A MIMO (multiple-input multiple-output) methodof wireless communication via a plurality of antennas, comprising:mapping symbols during a duration of each plural consecutive frames ofeach of a plurality of first data streams to frames of a plurality ofsecond data streams; and a step of varying the mapping during theduration of each of the plural consecutive frames of each of theplurality of first data streams.
 32. An electronic storage mediumstoring program instructions which when executed by a processor in aMIMO (multiple-input multiple-output) communication device for wirelesscommunication system, causes the processor to execute the stepscomprising: mapping symbols during a duration of each plural consecutiveframes of each of a plurality of first data streams to frames of aplurality of second data streams; and varying the mapping during theduration of each of the plural consecutive frames of each of theplurality of first data streams.
 33. A MIMO (multiple-inputmultiple-output) method of wireless communication via a plurality ofantennas, comprising: generating a plurality of first data streams, inwhich each first data stream includes a plurality of frames, and inwhich each frame includes a plurality of symbols; mapping symbols withineach of plural consecutive frames of each of the first data streams toframes of a plurality of second data streams based on at least onematrix, including a mapping matrix; and varying the at least one matrixover a duration of each of the plural consecutive frames of theplurality of first data streams to vary mapping of the plurality ofsymbols of each of the plural consecutive frames of the plurality offirst data streams to different of the plurality of second data streams,and in which one of the first and second data streams is coupled to theplurality of antennas.